Generally, the above-mentioned electronic memory cards use EEPROM or flash EPROM type memories which have the double advantage of being non volatile and electrically erasable, therefore rewritable. However, in some applications, these memories may be corrupted due to, in particular, an accidental interruption of the power supply during operation, leading to the loss of earlier data areas without writing new data in the said data areas.
This risk is especially important in the applications, such as the electronic memory cards, where the said memory is embedded in an object which depends on an external power source from which it may be separated at any time by withdrawal, deliberate or not.
The international patent application published under the number WO 97/25743 concerns a method for the secure updating of an EEPROM memory. In order to prevent the loss of sensitive data, for example if a power cut occurs during the updating, a method is provided, which includes saving the data to be updated in a backup region, programming a descriptor field for said region erasing the descriptor field for the following region of the back up memory, enabling an indicator corresponding to the back up region, updating the data, and disabling the indicator if the operation has been successful. The backup region is different every time. It is defined by scanning the backup memory and identified as the first region of the backup memory having an erased indicator. When the power supply is restored, the presence of an enabled indicator is systematically checked for, and the data saved in the corresponding regions are sent back to the main memory.